In semiconductor devices serving as power modules, semiconductor elements made of, for instance, silicon (Si) or silicon carbide (SiC) are used. Heat from such a semiconductor element, whose temperature needs to be kept at or below a predetermined temperature, should be efficiently dissipated.
In view of heat dissipation, a power module has been conventionally proposed that includes a cooler joined to the semiconductor element with an insulating substrate interposed therebetween. The insulating substrate has a one-piece structure composed of an insulating ceramic plate having high heat conductivity and conductive plates of metal having high heat conductivity disposed on both surfaces of the insulating ceramic plate. The insulating ceramic plate is made of, for instance, silicon nitride, aluminum nitride, or alumina. The conductive plate is made of, for instance, aluminum (including an alloy of aluminum, and so forth) or copper (including an alloy of copper, and so forth).
The semiconductor element is joined to one surface of the insulating substrate with a sintered metal, such as sintered Ag, interposed therebetween. The cooler is directly or indirectly joined to the other surface of the insulating substrate with a joining material, such as solder, interposed therebetween.
Meanwhile, semiconductor elements have been proposed in order to reduce the deformation of a resin that seals the semiconductor device. This deformation results from temperature changes in the external environment for instance. For instance, a semiconductor element having a bending strength degree of 100 MPa or more and 1000 Mpa or less is provided as a stress reliever.
A stress reliever in Patent Document 1 is composed of a semiconductor element disposed on a main surface of an insulating substrate and having a bending strength degree of 100 MPa or more and 1000 Mpa or less.